The generation of a known frequency is common in many commercial applications, including radio equipment, mobile phones, two way radios, television and radio frequency tuners. The need for digital control in such tuners has brought about dedicated phase locked loop integrated circuits which are expensive. These circuits have limitations as they have a predetermined discrete number of frequencies and pre-determined range of frequencies which they can generate. Such an arrangement is commonly seen when tuning a digital car radio where the FM frequency changes in steps of typically 0.1 MHz over a 20 MHz range.
Frequency control is also used in motor controllers, particularly in stepper and DC motor applications where a clock signal controls the speed of the motor. Varying the frequency of the clock signal controls the speed of the rotor. There are many established methods of translating the frequency of a clock signal to drive many different types of electrical motors and many commercially available integrated circuits which perform such translation. Conventional stepper controllers can typically only produce around 250 different predetermined stepping rates so that when the stepping rate needs to be changed it can only be done in a stepwise fashion. Accordingly, it is impossible to obtain a smooth change from one stepping rate to another, which is highly desirable in some applications.